I had similar problem. The LFS that's not really local keeps their water at 1017 and 82 degrees. My tank is 1025 and 77 degrees. I have tested the water after opening the bag and the ammonia was .5 A long acclimation in that high ammonia is not good, I have checked other samples with similar readings. I set my QT tank to the LFS parameters.
I bring a cooler with a heater very small power head and matching water. I don't let them bag the fish I have them put it in a specimen container and box that came with it. The fish goes right into cooler after checking sample water and cooler water as long as its very close I drop him in. Into the QT tank and acclimate over two weeks to match my DT, two weeks later into the DT. Never lost a fish after that.
I know extreme, but hey I was tired of loosing fish and it worked. Now I only buy fish from stores that keep their fish tanks at 1024, much cheaper and much less of a pain in the butt. I never said I was a fast learner, but I am persistent.